Re: Destructor question

[Matthew Heaney <matthew_heaney@acm.org>]

I give an example of how to implement a dispatching constructor in my
Nov 1998 post (with the subject "No subject", unfortunately) to the ACM
patterns archive.

<http://www.acm.org/archives/patterns.html>

The post itself is titled Yet Another Visitor, and shows how to
implement a tagged type with a private operation ("method") that
dispatches on the tag of the item, and frees the storage associated with
that object.

The type Composite_Equipment is very much like your container type: it's
a container that contains class-wide objects.

If you have trouble locating the post in the archive, send me your real
email address and I'll send it to you.

Matt



Rusnak <bogus@nowhere.com> writes:

> Now to the more important question:  I assume that IF I am going to use the
> Ada.Finalization package, that all my tagged records should be based off of
> the Controlled type within that package.  I would may also have to override
> the Finalize procedure since a derived class could allocate memorey for new
> attributes of the tagged record.  The Finalize, Initialize, and Ajust
> procedures do NOT take an access type however.  What I  have is an array of
> access values to a "'Class" type, and I need to deallocate the memory
> associated with each of the access values.  One cannot write an
> Unchecked_Deallocation for a "'Class" object (this makes sense).  What I
> need is to write is a dispaching procedure (i.e. a mehotd of a class) like
> the following:
> 
>     Given a type Instance which is an abstract tagged record and a type
> Object which is of type access all Instance and a type Class_Object which
> is of type access all Instance'Class,
> I would like to define a procedure:
> 
>     procedure Deallocate(The_Object : in out Object) is abstract;
> 
> which is dispatching.  The compiler certainly lets me declare such a
> procedure, but I can never use it, since it cannot accept a  parameter of
> type Class_Object to get it to dispatch.  Another solution is possible, but
> the above solution (if "implementable") would be the cleanest  and least
> intriusive way to go.
> 
> On another note,  if i override a proceudre in a derived class, how can I
> "chain" it to its super class (i.e.,  call  within the procedure the super
> class procedure which it overrides)?  I could certainly see the use in
> chaining  the Initialize procedure of the Controlled class mentioned
> above.  Explicit casting doesn't seem to work, and casting is not a very
> desirable solution anyway.
> 
> -John